The present invention relates to a novel phosphate group-containing resin and a water based metallic coating material composition comprising the above phosphate group-containing resin.
A water based metallic coating material containing a metallic pigment such as aluminum flake has the problem that the metallic pigment is brought into contact with a large amount of water contained in the coating material and corroded to generate hydrogen gas. In order to solve this problem, it is proposed that phosphoric acid esters are added to a water based metallic coating material to protect the surface of a metallic pigment with the phosphoric acid esters making use of an adsorptive action exerted by an acidic hydroxyl group bonded to a phosphorus atom of the above esters to inhibit reaction caused by direct contact of water with the metallic pigment. However, it is difficult to inhibit this reaction over a long period of time in a water based metallic coating material comprising such phosphoric acid esters, and a metallic coating film formed has the defect that an adhesive property, a water resistance, a chipping resistance and a metallic finish feeling are not satisfactory.
Disclosed respectively are a water based metallic coating material comprising an aluminum flake treated with a phosphoric acid ester in Japanese Patent Application Laid-Open No. 168670/1983, a water based metallic coating material comprising a phosphoric acid ester of caprolactone in Japanese Patent Application Laid-Open No. 29607/1986, a water based metallic coating material comprising a reaction product of orthophosphoric acid and an epoxy compound in Japanese Patent Application Laid-Open No. 47771/1986, a water based metallic coating material comprising a phosphate-containing acryl polymer obtained from orthophosphoric acid and a glycidy group-containing acryl polymer in Japanese Patent Application Laid-Open No. 190765/1989 and a water based metallic coating material comprising a polymer of styrene and allyl alcohol and a reaction product of p-t-amylphenol and orthophosphoric acid or phosphorus pentaoxide in Japanese Patent Publication No. 46624/1990. However, all of these water based metallic coating materials have the defect that the coating films thereof are not satisfactory in an adhesive property, a water resistance and a metallic appearance.
It has been found that a phosphate group-containing resin which is a copolymer of two kinds of some specific phosphate group-containing polymerizable monomers and a polymerizable monomer having two tertiary alkyl groups in a molecule is excellent in an adsorptive property to the surface of a metallic pigment and effective for inhibiting a reaction of water with a metallic pigment over a long period of time and that a coating film formed from a water based metallic coating material comprising such phosphate group-containing resin is excellent in performances such as an adhesive property, a water resistance, a chipping resistance and a metallic finish feeling.
Thus, according to the present invention, provided is a phosphate group-containing resin obtained by copolymerizing:
(a) a polymerizable monomer having a phosphate group represented by a formula [xe2x80x94OPO(OR)(OH)] (wherein R represents a hydrocarbon group having 4 to 10 carbon atoms),
(b) a polymerizable monomer having a phosphoric acid group represented by a formula [xe2x80x94OPO(OH)2] and
(c) a (meth)acrylate base polymerizable monomer having two tertiary alkyl groups in a molecule, which is represented by: 
wherein X represents hydrogen or methyl.
Further, according to the present invention, provided is a water based metallic coating material composition comprising the phosphate group-containing resin described above and a metallic pigment.
The phosphate group-containing resin and the water based metallic coating material composition which are provided by the present invention shall be explained below in further details.
The polymerizable monomer (a) is a phosphoric acid diester compound having each at least one phosphate group represented by a formula [xe2x80x94OPO(OR)(OH)] and polymerizable double bond in a molecule, wherein R represents a hydrocarbon group having 4 to 10 carbon atoms, and to be specific, it includes, for example, linear or branched chain alkyl groups such as butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, hexyl, octyl, 2-ethylhexyl, decyl and isodecyl.
Included in the polymerizable monomer (a) are those obtained by reacting, for example, one acidic hydroxyl group contained in a phosphoric acid monoester represented by (HO)2PO(OR), for example, phosphate such as monobutyl phosphate (Rxe2x95x90C4H9) and monoisodecyl phosphate (Rxe2x95x90C10H21) with a glycidyl group-containing compound having a polymerizable double bond, for example, glycidyl acrylate and glycidyl methacrylate.
The polymerizable monomer (b) is a compound having each at least one a phosphoric acid group represented by a formula [xe2x80x94OPO(OH)2] and polymerizable double bond in a molecule, and to be specific, it includes, for example, (2-acryloyloxyethyl) acid phosphate, (2-methacryloyloxyethyl) acid phosphate, (2-acryloyloxypropyl) acid phosphate and (2-methacryloyloxypropyl) acid phosphate.
The polymerizable monomer (c) is a compound represented by: 
(wherein X represents hydrogen or methyl) in a molecule, and it has two tertiary alkyl groups in a molecule, in which three methyl groups are bonded to one carbon atom. Use of this monomer (c) makes it easy to allow metallic flakes to be aligned parallel to the coated face in the water based metallic coating material of the present invention and makes it possible to elevate the metallic appearance of the coating film.
The phosphate group-containing resin of the present invention is obtained by copolymerizing as essential components, the polymerizable monomer (a), the polymerizable monomer (b) and the polymerizable monomer (c) each described above, and if necessary, the other polymerizable monomer (d) in addition thereto can be used in combination as a copolymerization component.
The other polymerizable monomer (d) is a compound having at least one polymerizable double bond in a molecule other than the polymerizable monomers (a), (b) and (c) each described above, and it includes compounds exemplified below.
1) (Meth)acrylate base monomers: for example, C1 to C24 alkyl esters of (meth)acrylic acid such as methyl methacrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate and lauryl (meth)acrylate.
2) Hydroxyl group-containing monomers: for example, C2 to C10 hydroxyalkyl esters of (meth)acrylic acid, such as hydroxyethyl (meth)acrylate and hydroxypropyl (meth)acrylate.
3) Carboxyl group-containing monomers: for example, unsaturated carboxylic acids and anhydrides thereof such as (meth)acrylic acid, maleic acid and maleic anhydride.
4) Other monomers: for example, vinyl aromatic compounds such as styrene, xcex1-methylstyrene and vinyltoluene, (meth)acrylonitrile and vinyl acetate.
The phosphate group-containing resin of the present invention can be produced by copolymerizing the polymerizable monomers (a) to (d) each described above in the presence of a polymerization initiator by a conventionally known method, for example, a solution polymerization method. A use proportion of these polymerizable monomers in copolymerization shall not strictly be restricted and can be changed over a wide range depending on characteristics desired to the phosphate group-containing resin produced. In general, it can fall in the following range based on the total amount of the polymerizable monomers (a) to (d):
The phosphate group-containing resin of the present invention can have a weight average molecular weight falling in a range of usually 3,000 to 100,000, preferably 5,000 to 50,000 and particularly preferably 5,000 to 30,000 and an acid value falling in a range of 20 to 140 mgKOH/g, particularly 40 to 120 mgKOH/g and further particularly 50 to 100 mgKOH/g originating in a phosphoric acid group. Further, the phosphate group-containing resin of the present invention can contain, if necessary, a carboxyl group and/or a hydroxyl group, and a content of these groups falls preferably in a range of 100 mgKOH/g or less, particularly 0 to 80 mgKOH/g in terms of an acid value originating in a carboxyl group and 0 to 120 mgKOH/g, particularly 15 to 100 mgKOH/g in terms of a hydroxyl value.
The phosphate group-containing resin provided by the present invention is very useful as a passivator for the metallic pigment in the water based metallic coating material and not only protects the metallic pigment from corrosion caused by reaction with water over a long period of time but also is excellent in an aligning property of the metallic pigment, and blending of the phosphate group-containing resin makes it possible to provide the water based metallic coating material composition which is excellent in a storage stability and excellent as well in coating film performances such as an adhesive property, a water resistance, a chipping resistance and a metallic finish feeling.
Thus, according to the present invention, provided is the water based metallic coating material composition comprising the phosphate group-containing resin of the present invention and the metallic pigment.
The water based metallic coating material composition of the present invention can be prepared by mixing and dispersing a base resin, a curing agent, the phosphate group-containing resin of the present invention and the metallic pigment and, if necessary, the other coating material additives in a water based medium.
Conventionally known resins which have so far been used for water based coating materials can be used as the base resin and includes, for example, water-soluble or water-dispersible reins such as alkyd resins, acryl resins, polyester resins and urethane resins. These resins have preferably cross-linking functional groups such as a hydroxyl group, a carboxyl group and an epoxy group in the molecules thereof The curing agent includes melamine resins, blocked polyisocyanate compounds, epoxy compounds and carboxyl group-containing compounds which can be reacted with these functional groups. A blending proportion of the base resin and the curing agent falls suitably in a range of 50 to 90%, particularly 60 to 80% in the former case and 50 to 10%, particularly 40 to 20% in the latter case each based on the total solid matter weight of the both.
The metallic pigment is a pigment which provides the coating film with a sparkling brilliant feeling and a light coherent pattern, and to be specific, capable of being used is at least one pigment selected from non-leafing type or leafing type aluminum (including deposited aluminum), aluminum oxide, copper, zinc, brass, nickel, mica and micas coated with titanium oxide and iron oxide. These metallic pigments are preferably flake-shaped. A blending proportion of the metallic pigment falls suitably in a range of usually 1 to 50 parts by weight, particularly 5 to 30 parts by weight per 100 parts by weight of the total of the base resin and the curing agent.
A blending proportion of the phosphate group-containing resin of the present invention falls suitably in a range of usually 0.1 to 15 parts by weight, particularly 0.5 to 10 parts by weight in terms of a solid matter per 100 parts by weight of the metallic pigment.
The phosphate group-containing resin of the present invention can be neutralized in advance with a base such as, for example, ammonia, dimethylamine, triethylamine, ethanolamine and dimethylethanolamine prior to blending with the coating material.
The water based metallic coating material composition of the present invention can be prepared, for example, by mixing and dispersing the base resin, the curing agent, the phosphate group-containing resin of the present invention and the metallic pigment each described above, if necessary, together with coating material additives such as a solid color pigment, an extender pigment, a hydrophilic organic solvent, a surface controlling agent and a settling inhibitor in a water based medium by a conventionally known method. In this case, the phosphate group-containing resin of the present invention and the metallic pigment are preferably mixed in advance, and the mixture thereof is preferably mixed and dispersed in a water based medium together with the base resin and the curing agent. To be more specific, the metallic pigment is homogeneously mixed with the phosphate group-containing resin solution of the present invention in which a solid matter content is controlled to 40 to 70% by weight in the proportion described above to adsorb the phosphate group-containing resin on the surface of the metallic pigment, and it is then neutralized with the base described above and dispersed. Then, it is preferably mixed and dispersed in water together with the base resin and the curing agent.
The coating material composition of the present invention can be coated directly on an article to be coated such as a metal-made or plastic-made automobile outside plate. In general, an undercoating material such as an electrodepositable coating material and, if necessary, an intermediate coating material are coated thereon in advance, and these coating films are cured. Then, the coating material composition of the present invention is preferably coated on the coated face thereof. A viscosity of the coating material composition of the present invention is controlled to a range of 10 to 30 seconds/Ford cup #4/20xc2x0 C. and preferably coated d by a method such as airless spray, air spray and an electrostatic method so that a film thickness is 10 to 40 xcexcm in terms of a cured film thickness.
The metallic coating film thus formed can usually be cured by heating at a temperature of about 100 to about 170xc2x0 C. for 10 to 40 minutes. Further, after curing this metallic coating film or without curing it, a clear coating material can further be coated on this metallic coated face.